This is a divisional application based on U.S. Ser. No. 09/272,883, filed Mar. 19 1999, which is a divisional application having priority in U.S. Ser. No. 08/706,085, filed Aug. 30, 1996 now U.S. Pat. No. 5,913,994.
Abrasive tools are reinforced with fibers to strengthen the tools and permit safe operation at high rotational speeds, especially in metal cut off, snagging and rough grinding operations. Abrasive tools designed for such operations are generally referred to as xe2x80x9cthin abrasive wheels.xe2x80x9d In the traditional manufacturing processes for such abrasive tools, woven fiberglass cloth discs are cut from cloth sheets and placed in molds for the wheel, below and on the top of a mix of abrasive grain and bond components. Wheels are then pressed in a mold and cured. Typical manufacturing processes for woven fiberglass cloth reinforcement are described in U.S. Pat. No. 4,800,685 to Haynes and U.S. Pat. No. 4,401,442 to Oide. Although these techniques yield uniform reinforcement across the diameter of the wheel, continuously covering the wheel from the central mounting hub to the wheel periphery, the manufacturing processes are characterized by high material waste (e.g., a minimum of 22%) and high labor costs.
In a non-traditional wheel design, partial reinforcement of a laminated composite wheel with woven fiberglass cloth has been suggested in U.S. Pat. No. 5,431,596 to Akita, et al. Higher wheel speeds have been achieved using woven rovings (non-twisted yarns) of fiberglass as disclosed in U.S. Pat. No. 3,838,543 to Lakhani. Woven fibers having higher strength and performance characteristics than fiberglass are used for reinforcement of wheels in U.S. Pat. No. 4,259,089 to Waizer and in U.S. Pat. No. 4,021,209 to Binkley, and fiber coatings are used for improved wheels containing woven fibers in U.S. Pat. No. 4,338,357 to Pichler, et al.
The non-woven fiberglass reinforcement techniques known in the art do not produce uniform, effective patterns of reinforcement. For example, the curved, preferably spiral or spirographic, path of fiberglass reinforcement disclosed in CA-A-2,108,094 to Rector would produce a wheel having a tangential reinforcement incapable of resisting the stress of a side load. The wheel also has fiber strands parallel to the grinding face of the wheel which would cause a variety of problems (e.g., splaying) in grinding operations. Similar problems with non-uniform reinforcement, failure to meet burst speed specifications, and lack of sufficient reinforcement at the grinding face of the wheel would result from the xe2x80x9cbicycle spokexe2x80x9d fiber design shown in DE-1,291,648 to Kistler, et al; and in the annular fiber pattern disclosed in U.S. Pat. No. 3,262,230 to Seymour, et al.
The use of short chopped fiber reinforcement as disclosed in, e.g., U.S. Pat. No. 4,989,375 to Henmi; U.S. Pat. No. 4,657,563 Licht, et al; U.S. Pat. No. 4,253,850 to Rue et al; GB-A-2,137,220 to Rands; and DE-A-1,502,655 to Ruggeberg, does not provide sufficient strength to reinforce thin abrasive wheels for more demanding high speed grinding operations.
Other non-woven fiber reinforcement techniques known in the art which could provide adequate wheel strength are not useful because they require complex operations with high labor or equipment costs. For example, a process for reinforcing wheels disclosed in U.S. Pat. No. 3,121,981 to Hurst requires the steps of: coating a fibrous sheet material containing abrasive grain with adhesive, placing parallel strands of reinforcing fibers on the tacky surface, coating the reinforcing fibers with a layer of an abrasive grain-organic bond mixture, drying and cutting the resulting laminate to the shape of the wheel, and stacking layers of the laminate with the reinforcing fibers oriented in different directions, and molding the stack to form a wheel. As disclosed in U.S. Pat. No. 4,164,098 to Akita, a floral design of long and short xe2x80x9cpetalsxe2x80x9d is used as an ancillary reinforcement near the hub of the wheel with woven fiberglass cloth reinforcement provided from the hub to the periphery of the wheel. These non-woven fiber processes employ excessive and costly steps to achieve wheel reinforcement.
It has now been discovered that methods of forming patterns of non-woven fibers on relatively inexpensive equipment may be used to yield uniformly reinforced thin abrasive wheels. Thin abrasive wheels, particularly raised hub wheels, reinforced with such uniform patterns of non-woven fibers have significantly improved resistance to hub push-out failure during grinding. operations. An apparatus has been developed to efficiently manufacture these non-woven fiber arrays.